1. Field of the Invention
The present invention relates to a microprobe constituted by a cantilever provided with a piezoresistive element on a surface of a semiconductor substrate and a sample surface measuring apparatus observing a very small area (nanometer order) of the sample surface by using the microprobe.
2. Description of the Prior Art
Currently, as a microscope for observing a very small area of nanometer order on a surface of a sample, there is known a Scanning Probe Microscope (SPM). In the field of SPM, an Atomic Force Microscope (AFM) uses a microprobe constituted by a cantilever provided with a stylus at a front end portion thereof and the stylus of the cantilever is made to scan along a surface of a sample constituting an observation object and atomic force (attractive force or repulsive force) caused between the surface of the sample and the stylus is detected as an amount of bending the cantilever to thereby measure the shape of the surface of the sample.
It is known that the above-described microprobe is classified into a microprobe of an optical lever type and a microprobe of a self detection type by a difference in a system of detecting the bending amount of the cantilever. The optical lever type microprobe referes to a microprobe used in a system in which a laser beam is irradiated to an end portion of the cantilever constituting the microprobe and the above-described bending amount is detected by measuring a change in an angle of reflection thereof. This system is also known as an optical lever detection system.
The optical lever type microprobe has the advantage that it is capable of being fabricated inexpensively in comparison with the self detection type microprobe. On the other hand, the optical lever type microprobe has the drawback that when it is used in an atomic force microscope, it is necessary to finely adjust an irradiation angle of a laser beam irradiated to the cantilever and a position of a photodiode for detecting a reflection beam from the cantilever and the like. In particular, which interchanging the cantilever which is frequently carried out, the fine adjustment must be carried out repeatedly, which is troublesome.
Meanwhile, the self detection type microprobe refers to a microprobe forming a piezoresistive element on the cantilever and capable of detecting the bending amount of the cantilever by measuring a variation in a resistance value thereof.
According to the self detection type microprobe, when used in an atomic force microscope, since a detector (piezoresistive element) for detecting the bending amount of the cantilever is formed at the microprobe per se, there is provided an advantage in which in interchanging the cantilever, the troublesome operation of adjusting the position of the detector is not necessary and the observation of a sample can be started swiftly. On the other hand, in comparison with the optical lever type microprobe, there is provided a drawback in which the constitution of the microprobe becomes complicated and the microprobe becomes difficult to provide inexpensively to a user.
FIG. 10 is a block diagram showing an outline constitution of an atomic force microscope using particularly the above-described self detection type microprobe in these microprobes. In FIG. 10, an atomic force microscope 200 comprises a microprobe 201 (corresponding to the above-described self detection type microprobe) provided with a sharpened stylus 202 directed toward a surface of a sample 203 at its front end portion, an XYZ actuator 210 for finely moving the sample relative to the microprobe 201 in the horizontal direction (X, Y direction) and the vertical direction (Z direction), an actuator drive amplifier 212 for generating an XYZ control signal for driving the XYZ actuator 210, a scanning signal generating unit for generating a signal (scanning signal) for finely moving the sample 203 at constant speed in a predetermined range in the above-described X and Y directions, a measuring unit 216 for acquiring a detection signal provided from a bending detecting portion (the above-described detector: piezoresistive element) on the microprobe 201, a reference value generating unit 128 for generating a detection value in a steady state of the above-described bending detecting portion, that is, a reference value for detecting irregularities of the surface of the sample 203, a comparator 220 for deriving an actual bending amount of the microprobe 201 by comparing signals respectively provided from the measuring unit 216 and the reference value generating unit 218 and a control unit 222 for generating a signal in correspondence with a displacement of the XYZ actuator 210 in Z direction based on a signal provided from the comparator 220.
A brief explanation will be given of operation of the atomic force microscope 200 as follows. First, the user fixes the sample 203 constituting the observation object onto a stage on the XYZ actuator 210 and attaches the microprobe 201 at a comparatively remote position above thereof. Normally, the microprobe 201 is arranged with an electrode terminal for taking out a signal from the above-described bending detecting portion at an end portion thereof disposed opposedly to the stylus 202 and on a face opposed thereto in the longitudinal direction, normally, the microprobe 201 is provided separately from the atomic force microscope as an attachable and detachable cartridge type one facilitating electric connection between the electrode terminal and the measuring unit 216 and fixing an end portion thereof on the side of the electrode terminal.
After preparation before observing the sample has been finished in this way, successively, it is necessary to make the microprobe 201 sufficiently proximate to the sample 203 to a degree that the stylus 202 produces atomic force between the stylus 202 and the surface of the sample 203. The proximity control is carried out firstly, while making the sample 203 being proximate to the stylus 202 by a Z-axis rough movement mechanism (not illustrated) in the XYZ actuator 210, by monitoring whether a predetermined amount of signal can be acquired from the above-described bending detecting portion by the measuring unit 216.
The Z-axis rough movement mechanism in the XYZ actuator 210 is instructed by a computer (not illustrated) for controlling operation of the atomic force microscope 200 under a predetermined condition via the user and is operated based on a Z control signal generated via the actuator drive amplifier 212.
Further, the above-described predetermined amount of signal acquired in the measuring unit 216 is a signal indicating detection of the atomic force between the stylus 202 and the surface of the sample 203 and is actually informed by a signal outputted from the comparator 220. In this case, the resistance value of the piezoresistive element per se constituting the bending detecting portion is varied by conditions other than bending such as temperature condition or the like and accordingly, the reference value of the reference value generating unit 218 constituting one of comparison objects of the comparator 220, provides a reference resistance value for removing the unnecessary variation information from a variation in the resistance value measured at the bending detecting portion.
After finishing the above-described proximity control, at the scanning signal generating unit 214, there is generated a scanning signal for instructing a movement in a predetermined range set on the computer, mentioned above, that is, in a plane range (XY range) in the XYZ actuator. Normally, the scanning signal is a signal for realizing so-to-speak raster scanning in which after finishing scanning operation in X direction while fixing a Y-axis point, the scanning is moved to a successive Y-axis point and the scanning operation in X direction is carried again.
The scanning signal is inputted to the actuator drive amplifier 212, amplified pertinently to current or voltage sufficient for driving the XYZ actuator 210 and thereafter inputted to the XYZ actuator 210 as an XY control signal. The XYZ actuator 210 actually moves the sample 203 on the stage in X and Y directions by inputting the XY control signal.
While repeating the movement of the sample 203 on the XY plane by the above-described XYZ actuator 210, the measuring unit 216 always acquires a signal from the bending detecting portion of the microprobe 201 and a signal in correspondence with the bending amount of the microprobe 201 is outputted from the comparator 220.
In this case, as measurement modes of the atomic force microscope 200, actually, there are various measurement modes of a height constant mode for maintaining constant a height between the stylus 202 and the sample 203 after the proximity control and regarding the bending amount of the microprobe 201 as an irregularity signal of the sample 203, and a bending constant mode for controlling a Z-axis fine movement mechanism (not illustrated) of the XYZ actuator 210 by a feedback control such that the bending amount of the microprobe 201 becomes constant and regarding a control signal required for the feedback control as the irregularity signal of the sample 203 and so on, however, it is assumed here that the bending constant mode is selected.
Therefore, the sample 203 is moved in a constant range on the XY plane and is finely moved in the Z-axis direction by feedback control of the Z-axis fine movement mechanism in the bending constant mode. Simultaneously therewith, the XY control signal and the Z control signal in accordance with operation of the above-described XYZ actuator 210 are inputted to a display apparatus (CRT) and a user can be informed of the surface information of the sample 203.
However, as mentioned above, the atomic force microscope 200 needs the XYZ actuator provided with the fine movement mechanism in the Z-axis direction in addition to the fine movement mechanism in X and Y directions for carrying out the fine movement control in the Z-axis direction, which constitutes a factor hampering downsized formation of the apparatus constituting the microscope. Further, the XYZ actuator is generally formed by piezoelectric elements and is not necessarily regarded to be provided with sufficient response speed, further, considerable power is needed for driving thereof and accordingly, even in the fine movement in the Z-axis direction, the fine movement constitutes a factor of hampering a reduction in power consumption.
Hence, in constituting the apparatus, there is known a microprobe provided with a Z-axis fine movement function on a cantilever in order to exclude the Z-axis fine movement mechanism by the actuator. FIG. 11 is a view showing a microprobe having the Z-axis fine movement function. In FIG. 11, a microprobe 300 is formed with the stylus 201 and a bending detecting portion 310 (piezoresistive element) at a first lever portion 302 enabling flexible bending by a free end and is formed with an actuator portion 320 on a second lever portion 304.
The actuator portion 320 comprises a piezoelectric element of ZnO or the like, is capable of elongating and contracting in the longitudinal direction of the second lever portion 304 by applying current, as a result, the second lever portion 304 is bent in a direction orthogonal to the plane by the elongating and contracting operation. That is, the fine movement of the microprobe 300 in the Z-axis direction is realized by the actuator portion 320 on the probe.
However, according to the microprobe having the Z-axis fine movement function as shown by FIG. 11, there are adopted piezoelectric elements similar to those in the conventional XYZ actuator as the actuator for realizing the Z-axis fine movement function and accordingly, power consumption cannot be reduced.
Further, the microprobe is very small and accordingly, by providing, on a silicon substrate constituting a base member thereof, in addition to the piezoresistive elements constituting the bending detecting portion, the piezoelectric members having a material quite different from the material of the piezoresistive element, there poses a problem in which not only steps of fabricating thereof become complicated but also a thickness of the cantilever portion is increased and it is difficult to ensure sufficient response speed.
The invention has been carried out in view of the drawback of the conventional technology and it is an object thereof to provide a microprobe enabling to finely move a cantilever by forming a piezoresistive element on the cantilever and a sample surface measuring apparatus using the microprobe.
A microprobe is constituted by a first lever portion having a free end formed with a stylus, a second lever portion projected with a first lever portion at a front end portion thereof and a support portion for supporting the second lever portion and a piezoresistive element for bending the second lever portion is provided on the second lever portion.